Relative intensity influences the degree of correspondence of jump squats and push jerks to countermovement jumps

The aim of this study was to determine the mechanical similarity between push jerk (PJ) and jump squat (JS) to countermovement jump (CMJ) and further understand the effect increasing external load may have on this relationship. Eight physically trained males (age 22 ± 3; height 176 ± 7 kg; weight 83 ± 8 kg) performed an unloaded CMJ followed by JS under a range of loads (10%, 25%, 35% and 50% 1RM back squat) and PJ (30%, 50%, 65% and 75% 1RM push jerk). A portable force platform and high speed camera both collecting at 250 Hz were used to establish joint moments and impulse during the propulsive phase of the movements. A standard inverse dynamics model was used to determine joint moment and impulse at the hip, knee and ankle. Significant correlations (p<0.05) were shown between CMJ knee joint moment and JS knee joint moment at 25% load and PJ knee joint moment at 30% and 50% load. Significant correlations were also observed between CMJ knee joint impulse and JS knee joint impulse at 10% load and PJ knee joint moment at 30% and 65% load. Significant correlation was also observed between CMJ hip joint impulse and PJ hip joint impulse at 30% load. No significant joint x load interaction was shown as load increased for either PJ or JS. Results from the study suggest partial correspondence between PJ and JS to CMJ, where a greater mechanical similarity was observed between the PJ and CMJ. This interaction is load and joint dependent where lower relative loads showed greatest mechanical similarity. Therefore utilising lower relative loads when programming may provide a greater transfer of training effect

PROXIMAL AND DISTAL CONSTRAINTS REDUCE DIMENSIONALITY OF VERTICAL JUMPING TASKS

The purpose of this study was to examine motor control strategies employed to control the degrees of freedom when performing a lower limb task with constraints applied at the hip, knee and ankle. Thirty-five individuals performed vertical jumping tasks: hip flexed, no knee bend and plantar flexed. Joint moment data from hip, knee and ankle was analysed using principal component analysis (PCA). In all, PCA performed, a minimum of two and maximum of six principal components (PCs) were required to describe the movement. A proximal to distal reduction in variability was only observed for the hip flexed and no knee bend conditions. Collectively, the results suggest a reduction in the dimensionality of the movement occurs, despite the constraints imposed within each condition and would suggest dimensionality reduction and motor control strategies are a function of the task demands

Segmental and Intersegmental Coordination Characteristics of a Cognitive Movement Control Test: Quantifying Loss of Movement Choices

Cognitive movement control tests are hypothesized to reveal reduced coordination variability, a feature of motor behaviour linked to clinical presentations. Exploration of this proposition via kinematic analysis of test pass and fail conditions is yet to be conducted. Kinematics (3D) were collected as 28 participants were qualitatively rated during nine trials of a cognitive movement control test. Ten female and two male participants passing the test were matched to twelve participants who failed (three males, nine females). Sagittal plane pelvis and knee angles were determined. Peak pelvic deviation and knee flexion maxima/minima were compared between groups. Classification tree analysis explored relationships between test failure and pelvis–knee intersegmental coordination strategy classifications derived from novel and traditional vector coding techniques. Coordination variability waveforms were assessed via SPM. Age, BMI, and knee flexion values did not differ between the groups (p > 0.05); however, participants rated as failing the test displayed greater pelvic deviation (p < 0.05). Classification tree analysis revealed a greater use of pelvic dominant intersegmental coordination strategies from both vector coding techniques (p < 0.001) by fail-group participants. The fail-group also displayed lower coordination variability for novel (p < 0.05), but not traditional (p > 0.05) vector coding technique waveforms, supporting the premise that the testing protocol may act as a qualitative approach to inform on features of motor behavior linked to clinical presentations

Jump test asymmetry profiles of elite trials cyclists.

Bike trials is a cycling discipline in which riders navigate a series of obstacle courses on their bikes. As many of the techniques used in trials riding are acyclic, riders will display a natural preference as to which foot is on the front pedal. The primary aim of this study was to try to identify if this unique riding style creates a sport-specific inter-limb asymmetry profile during a range of common jump tests. Eight elite trials riders (mean age 20.0 ± 0.9 years, height 178.5 ± 6.8 cm, weight 76.1 ± 10.4 kg) completed three repetitions each of countermovement jump, single leg countermovement jump and single leg hop tests. There were no significant asymmetries between the overall group means for the jump tests (absolute asymmetry: countermovement jump 5.4 ± 3.6%; single leg countermovement jump 10.0 ± 5.4%; and single leg hop 5.9 ± 4.0%). There were however significant (p<0.05) individual asymmetries found in all of the jump tests and meaningful asymmetries (percentage asymmetry greater than coefficient of variation) in both of the single leg tests. The direction of asymmetry was shown to be variable across the different tests (Fleiss’ Kappa = -0.34). Some participants also showed meaningful and significant differences in the movement strategies used within a test, though again there were no significant differences in the group means. The findings suggest inter-limb asymmetries are highly task specific and there was no evidence to suggest that trials riders develop specific asymmetries due to the asymmetrical physical demands of their sport

Differences in Motor Control Strategies of Jumping Tasks, as Revealed by Group and Individual Analysis.

The aim of this study was to investigate the motor control strategies adopted when performing two jumping tasks with different task demands when analysed at an individual and group level. Twenty-two healthy individuals performed two jumping tasks: jumping without the use of an arm swing (CMJnas) and jumping starting in a plantar flexed position with the use of an arm swing (PF). Principal component analysis (PCA) was performed using hip, knee and ankle joint moment data on individual (PCAi) and group data (PCAc). The results demonstrate that a greater number of PCs are required to explain the majority of variance within the dataset in the PF condition at both an individual and group level, compared to CMJnas condition. Although common control strategies were observed between the two jumping conditions, differences in the organisation of the movement (PC loading coefficients) were observed. Results from the group analysis did not completely reflect the individual strategies used to perform each jumping task and highlight the value in performing individual analysis to determine emergent control strategies

Optimised force-velocity training during pre-season enhances physical performance in professional rugby league players

The effectiveness of 8-week force-velocity optimised training was assessed in highly trained professional rugby league (RL) athletes. Players (age 24 ± 3 years; body mass 94.9 ± 21.6 kg; height 181.3 ± 6.0 cm) were strength-matched and assigned to a force-velocity optimised group (OP; n=15) or a general strength-power group (GP; n=14). Tests conducted pre-and post-training included 10-m, 20-m sprints, 3 repetition-maximum (3RM) squat and squat jumps (SJ) over five load conditions to ascertain vertical force-velocity relationship. ANCOVA revealed there was a group effect for force-velocity deficit (P<0.001), with the OP two-fold greater than the GP group (OP pre: 51.13 ± 31.42%, post: 62.26 ± 31.45%, GP pre: 33.00 ± 19.60%, post: 31.14 ± 31.45%, P<0.001). There were further group effects for 3RM squat (OP pre: 151.17 ± 22.95kg, post: 162.17 ± 24.16kg, GP pre: 156.43 ± 25.07kg, post: 163.39 ± 25.39kg, P<0.001), peak power (OP pre: 3195 ± 949W, post: 3552 ± 1033W, GP pre: 3468 ± 911W, post: 3591 ± 936W, P<0.001), and SJ (OP pre: 39.79 ± 7.80cm, post: 42.69 ± 7.83cm, GP pre: 40.44 ± 6.23cm, post: 41.14 ± 5.66cm, P<0.001). Prescribing F-V deficit training is superior for improving physical performance within highly trained RL players

Principal Component Analysis Reveals the Proximal to Distal Pattern in Vertical Jumping Is Governed by Two Functional Degrees of Freedom

The successful completion of motor tasks requires effective control of multiple degrees of freedom (DOF), with adaptations occurring as a function of varying performance constraints. In this study we sought to compare the emergent coordination strategies employed in vertical jumping under different task constraints [countermovement jump (CMJ) with arm swing-CMJas and no arm swing-CMJnas]. In order to achieve this, principal component analysis (PCA) was conducted on joint moment waveform data from the hip, knee and ankle. This statistical approach has the advantage of analyzing the whole movement within a time series and reduces multidimensional datasets to lower dimensions for analysis. Both individual and group analyses were conducted. For individual analysis, PCA was conducted on combined hip, knee, and ankle joint moment data for each individual across both CMJnas (thirty-eight participants), and CMJas (twenty-two participants) conditions. PCA was also performed comparing all data from each individual across CMJnas and CMJas conditions. The results revealed a maximum of three principal components (PC) explained over 90% of the variance in the data sets for both conditions and within individual and group analyses. For individual analysis, no more than 2PCs were required for both conditions. For group analysis, CMJas required 3PCs to explain over 90% of the variance within the dataset and CMJnas only required 2PCs. Reconstruction of the original NJM waveforms from the PCA output demonstrates a greater loading of hip and knee joint moments to PC1, with PC2 showing a greater loading to ankle joint moment. The reduction in dimensions of the original data shows the proximal to distal extension pattern in the sagittal plane, typical of vertical jumping tasks, is governed by only 2 functional DOF, at both a group, and individual level, rather than the typically reported 3 mechanical DOF in some forms of jumping

Task Demand Changes Motor Control Strategies in Vertical Jumping.

The purpose of this study was to examine the motor control strategies employed to control the degrees of freedom when performing a lower limb task with constraints applied at the hip, knee, and ankle. Thirty-five individuals performed vertical jumping tasks: hip flexed, no knee bend, and plantar flexed. Joint moment data from the hip, knee, and ankle were analyzed using principal component analysis (PCA). In all PCA performed, a minimum of two and maximum of six principal components (PC) were required to describe the movements. Similar reductions in dimensionality were observed in the hip flexed and no knee bend conditions (3PCs), compared to the plantar flexed condition (5PCs). A proximal to distal reduction in variability was observed for the hip flexed and no knee bend conditions but not for the plantar flexed condition. Collectively, the results suggest a reduction in the dimensionality of the movement occurs despite the constraints imposed within each condition and would suggest that dimensionality reduction and motor control strategies are a function of the task demands

Reliability and validity of velocity measures and regression methods to predict maximal strength ability in the back-squat using a novel linear position transducer

The purpose of this study was to examine the reliability of load-velocity profiles (LVPs) and validity of 1-repetition maximum (1-RM) prediction methods in the back-squat using the novel Vitruve linear position transducer (LPT). Twenty-five men completed a back-squat 1-RM assessment followed by 2 LVP trials using five incremental loads (20%–40%–60%–80%–90% 1-RM). Mean propulsive velocity (MPV), mean velocity (MV) and peak velocity (PV) were measured via a (LPT). Linear and polynomial regression models were applied to the data. The reliability and validity criteria were defined a priori as intraclass correlation coefficient (ICC) or Pearson correlation coefficient (r) . 0.70, coefficient of variation (CV) 410%, and effect size (ES) \0.60. Bland Altman analysis and heteroscedasticity of errors (r2) were also assessed. The main findings indicated MPV, MV and PV were reliable across 20%–90% 1-RM (CV \ 8.8%). The secondary findings inferred all prediction models had acceptable reliability (CV \ 8.0%). While the MPV linear and MV linear models demonstrated the best estimation of 1-RM (CV \ 5.9%), all prediction models displayed unacceptable validity and a tendency to overestimate or underestimate 1-RM. Mean systematic bias (27.29 to 2.83 kg) was detected for all prediction models, along with little to no heteroscedasticity of errors for linear (r2 \ 0.04) and polynomial models (r2 \ 0.08). Furthermore, all 1-RM estimations were significantly different from each other (p \ 0.03). Concludingly, MPV, MV and PV can provide reliable LVPs and repeatable 1-RM predictions. However, prediction methods may not be sensitive enough to replace direct assessment of 1-RM. Polynomial regression is not suitable for 1-RM prediction

Reliability of the Coach’s Eye Goniometer Application during Squat Exercise

This study examined the test re-test, intrarater and interrater reliability of joint kinematics from the Coach’s Eye smartphone application. Twenty-two males completed a 1-repetition maximum (1-RM) assessment followed by 2 identical sessions using 5 incremental loads (20%-40%-60%-80%-90% 1-RM). Peak flexion angles at the hip, knee, and ankle joints were assessed using 1 experienced practitioner and 1 inexperienced practitioner. The acceptable reliability thresholds were defined as intraclass correlation coefficient (ICC) (r) > 0.70 and coefficient of variation (CV) ≤ 10%. The test re-test reliability of peak hip and knee flexion were reliable across 20-90% 1-RM (r > 0.64; CV 0.70; CV 0.11). The intrarater reliability was near perfect (r > 0.90) except for peak ankle flexion (r > 0.85). The interrater reliability was nearly perfect (r > 0.91) except for hip flexion at 80% 1-RM and ankle flexion at 20% (r > 0.77). Concludingly, the Coach’s Eye application can produce repeatable assessments of joint kinematics using either a single examiner or 2 examiners, regardless of experience level. The Coach’s Eye can accurately monitor squat depth